Smokeless exothermic hot topping compositions

ABSTRACT

Smokeless exothermic hot topping compositions are provided for application to the metal hot top of a cast ingot or a casting riser to improve the yield of usable metal or inhibit piping. Exothermic compositions containing aluminum, iron oxide and inert filler materials are disclosed which produce no visible smoke when used as hot topping materials.

ilnite States atent 1191 Davis et al.

1 1 SMOKELESS EXOTHERMIC HOT TOPPING COMPOSITIONS 22 Filed: Oct. 31, 1973 21 App]. No.: 411,401

52 US. Cl 106/3827, 164/53, 249/202, 249/010. 5 51 Int. Cl ..B28b 7/36 581 Fieldof Search 106/3827; 164/53; 249/202, DIG. 5

[56] References Cited' UNITED STATES PATENTS 3,025,153 3/1962 CrOSS 164/53 X Feb. 18, 1975 Primary ExaininerLewis T. Jacobs Attorney, Agent, or FirmWood, Herron & Evans [57] ABSTRACT Smokeless exothermic hot topping compositions are provided for application to the metal hot top of a cast ingot or a casting riser to improve the yield of usable metal or inhibit piping. Exothermic compositions containing aluminum, iron oxide and inert filler materials are disclosed which produce no visible smoke when used as hot topping materials.

23 Claims, N0 Drawings 1/1973 Wiley 106/3827 SMOKELESS EXOTIIERMIC HOT TOPPING COMPOSITIONS BACKGROUND OF THE INVENTION mold. Hot top boards or casings usually insulate the top 1 /2 to 2 feet ofthe cast ingot sides; and exothermic materials are added to the top of the cast metal to provide heat and'insulate the metal surface. Hot top boards and exothermic topping materials together maintain a reservoir of molten metal to feed the shrinkage normally encountered in the center of a solidifying ingot top. This shrinkage is a phenomenon commonly called piping and, therefore, exothermic compositions are sometimes referred to in the art as anti-piping" compositions During subsequent rolling, the top or riser portion of the metal ingot is sheared off and discarded and the balance of the ingot is processed into the desired shapes.

Most known ingredients used in exothermic materials include oxidizers, fuels, inert ingredients, and fluxes. Oxidizers include mill scale (Fe O iron ore (Fe O alkali metal nitrates, manganeseor chromium oxide (or other metal oxides), metal chlorates or picrates; fuels include aluminum, ferrosilicon, titanium, magnesium, silicon or alloys thereof, carbon (in the form of coke, charcoal, coal, charred oat hulls, etc.), organic compounds (resin binders), and the like; inert ingredients include sand, grog, slags, clay binders, alumina cement, perlite, vermiculite, or the like; and fluxes include sodium chloride, fluorides such as calcium fluoride or sodium fluoride. Representative prior art patents which disclose such compositions include British Pat. Nos. 673,605; 745,668; 769,719; 852,377; 870,668;

969,311; Canadian Pat. No. 631,077; U.S. Pat. Nos. 2,514,793; 2,791,816 2,850,373; 2,937,425; 3,025,153; 3,104,996; 3,132,061;

3,183,562; 3,198,640; 3,347,721; and 3,672,918.

Conventional exothermic topping compositions produce considerable smoke and fume during use. Foundry workers are subjected to risky working conditions and health hazards caused by such smoke. Federal and state statutes have been enacted which require safer and healthier working conditions in plants and foundries. Attempts have been made in the past to overcome the hazards of smoke and fume caused by exothermic topping materials. For example, it has been proposed in U.S. Pat. No. 3,713,852 that smoke evolution can be minimized in certain exothermic compositions by critically controlling particle sizes of specific oxidizers and fuels and maintaining the ingredients of such compositions within specified compositional limits. Another proposal has been to employ organic additives to consume fumes produced by certain exothermic compositions as illustrated by U.S. Pat. No. 3,728,102. There is still however a critical need for an exothermic topping composition which is smokeless and which still provides other essential functional requirements.

SUMMARY OF THE INVENTION This invention is directed to an exothermic hot topping composition for use in the primary production or casting of metal, particularly iron or steel. Exothermic compositions have been discovered which are completely smokeless and provide adequate feeding of an ingot hot top or cast metal riser. In fact, actual production runs for ingot steel castings have demonstrated that exothermic compositions of this invention perform without producing any visible smoke. In contrast, known exothermic hot topping materials produce considerable smoke.

This invention is predicated in part upon the discovery that certain oxidizer, fuel and inert filler materials can be proportioned to provide smokeless exothermic compositions. In a preferred form, the compositions contain mill scale (Fe O,), aluminum and inert filler materials. These compositions contain an effective amount of an oxide of iron up to about 50% by weight and an effective amount of fuel of aluminum or aluminum alloy providing up to about 15% by weight aluminum and the balance being predominantly composed of inert filler materials. These components are proportioned to provide smokeless compositions. Smokeless as the term is broadly used herein to characterize compositions of this invention means no visible smoke or only trace amounts of visible smoke. However, compositions are advantageously provided as mentioned above in accord with the principles of this invention which produce no visible smoke. Smokeless as it applies to compositions of this invention can also be equated herein to a Ringelmann number less than 1 or equivalent opacity of less than 20%.

Generally, smoke is considered to consist of the gaseous products of burning organic materials, such as wood, coal, or tobacco, rendered visible by the pres ence of small particles of carbon, which finally settle as soot. However, in the field of physical chemistry, any suspension of solid particles in a gas is termed smoke. Sometimes, however, the term smoke is used to include fume, vapor, or dust that resembles smoke. In this application, the term smoke will include the latter I meanings. The Ringelmann Smoke Chart and equivalent opacity is used herein to read visible emissions of smoke. The Ringelmann Chart was developed by Maximilian Ringelmann in the late 1800s and has been a useful tool ever since, at least in controlling visible emissions, which constitutes the nuisance form of air pollution. The Ringelmann Chart is thoroughly covered in the Bureau of Mines Information Circular No. 8333 (May, 1967), and this Circular is incorporated herein 1 by reference to ascertain smoke emissions by Ringel mann number and opacity. Another article incorpo' rated herein by reference is Reading Visible Emission by Jerome J.'Rom, U.S. Department of Health, Education and Welfare, April 1968. The Ringelmann system isvirtually a scheme whereby graduated shades of gray, varying by five equal steps between white and black, may be accurately reproduced by means of a rectangular grill of black lines of definite width and spacing on a white background. The rule by which charts may be reproduced is as follows:

Card 0 All white.

Card 1 Black lines 1 mm thick,,l0 mm apart, leaving white spaces 9 mm square.

Card 2 Lines 2.3 mm thick, spaces 7.7 mm square.

Card 3 Lines 3.7 mm thick, spaces 6.3 mm square.

- Card 4 Lines 5.5 mm thick, spaces 4.5 mm square.

Card 5 All black.

The chart, as distributed by the Bureau of Mines, provides the shades of cards 1, 2, 3, and 4 on a single sheet, which are known as Ringelmann No. l, 2, 3, and 4, respectively. To use the chart, it is supported on a level with the eye, at such distance from the observer that the lines on the chart merge'into shades of gray, and as nearly as possible in line with a smoke source. The observer glances from the smoke, as it issues from the smoke source, to the chart and notes the number of the chart most nearly corresponding with the shade of the smoke, then records this number with the time of observation. A clear source is recorded as No. 0, and I percent black smoke as No. 5. Although the Ringelmann Chart is only useful in evaluating black or gray emissions, a principle of equivalent opacity was developed which makes possible the application of the Ringelmann principle to other colors of smoke. Opacity simply means the degree to which transmitted light is obscured. Below is the relationship between Ringelmann number and opacity:

Ringclmann No. Opacity Preferred operable ranges of main components are about -45% of an oxide of iron, about 91 3% aluminum fuel as aluminum metal or alloys thereof with the balance of predominantly inert materials. These main components are finely divided to permit blending for uniformity of reaction. However, the mesh sizes of iron oxide, aluminum and inert fillers can vary over wide ranges as the examples demonstrate to achieve smokeless compositions and, therefore, mesh sizes of these components are not critically limiting upon the principles ofthis invention. In another of its aspects, a minor amount of granular graphite can be incorporated in the exothermic composition to provide an early ignition of the exothermic reaction without deleteriously affecting I its smokelessness. An amount of graphite on the order of about 1 to about 4% by weight has been found to fulfill these purposes when employed in the compositions of this invention.

The inert filler materials are selected from a class of diverse materials, particularly refractory materials in granular form such as fire clay, fire-clay grog, bauxite, olivine, perlite, expanded perlite, silica flour, silica sand and the like. The mesh sizeof such inert filler materials can vary over considerable ranges. It is preferred, however, to use coarse mesh sizes whose average mesh size is within the range of about l2 to about +100 to insure smokelessness. Finer particles have a tendency to cause melting or higher reaction temperatures of the exothermic compositions in use which in turn has been found to induce the formation of smoke. The mesh sizes for inert materials, however, can be varied within the essential compositional parameters of this invention as willbe appreciated by the working examples and description of this invention.

An additional advantage is secured by the compositions of this invention when an insulating slag forming material is included with the main components. The inert filler material can also function as an insulating slag forming material. In a preferred form, about 5-l5% by weight of expanded perlite is used as a slag forming additive which provides an insulating property to the compositions in use. Also, it is desirable to include binders which permit pelletization of the exothermic compositions to reduce dust formation. Binders such as fire clay are employed to assist in pelletization.

In accord with one best mode of operation, an exothermic hot topping material that is completely smokeless is provided according to the principles of this invention when that composition consists essentially of about 35-42% by weight mill scale, I l-l3% by weight of aluminum, 30% by weight raw fire clay, about l0% by weight expanded perlite, about 5% by weight fireclay grog and about 3% by weight graphite. This composition is especially preferred in preparing pelletized materials as just mentioned in accordance with the above procedures. Each of the ingredients performs certain functions. The mill scale (Fe O provides the oxygen for the combustion of fuel, that is, the aluminum and the graphite. The expanded perlite serves to slow down the reaction and also acts as an insulator to help retain most of the heat in the steel ingot material.

The fire clay is added as a binder to permitpelletizing of the damp mixture and the fire-clay grog is added as a compatible inert ingredient. The perlite, fire clay and fire-clay grog all act as inert ingredients that decrease the reaction rate and help retain the evolved heat in the steel ingot by their insulating properties in the slag. Of course, when granular materials are desired rather than the pelletized form, the compositional content of the inert refractory materials can be varied as the examples below demonstrate. For example, if pelletization is unnecessary to reduce dust, the fire clay could be replaced with other'materials that would improve the ignition characteristics of the mixture and the insulating properties of the resulting slag. Again, pelletization has the advantage of eliminating dust and may be particularly suited where it is important to reduce the amounts of dust as well as reduction of smoke or fumes.

A main finding in practicing this invention is the control of the compositional limits both of iron oxide oxidizer and aluminum fuels below certain critical amounts. An operable exothermic amount of oxide of iron up to about 50% by weight and aluminum fuel up to about 15% by weight has been found essential in providing smokelessness. The ratios of oxidizer and fuel will vary within these ranges of amounts. A stoichiometric ratio of about 3.2 to 1 of iron oxide to aluminum fuel is satisfactory, however, it is not critically essential to a practice of this invention. It has been discovered that amounts of iron oxide can be increased within the specified compositional range provided the aluminum fuel is decreased to achieve a smokeless composition. For example, as the amount of iron oxide is increased above about 40% towards about 50% by weight, the aluminum fuel should be decreased from about 15% by weight towards about 10% by weight to achieve smokelessness. These and other variations'of the parameters of this invention will be further understood by reference to the examples which follow.

EXAMPLES 1l l Exothermic hot topping compositions of this invention were prepared as lOOO-gra'm samples in Examples ll 1 containing ingredients in weight percent as listed in Table I as follows. All compositions of Table I additionally contained 30% raw fire clay, except Examples 5 and '6' in which 27% raw fire clay was used. These compositions were ignited on IOO-pound inductionfurnace heats of carbon steel maintained at about 29003000F by supplying a small amount of power to the induction coil.

All samples were prepared in the form of Ar-inch or small pellets. The mill scale (Fe O,) was first screened through a /2-inch-mesh screen, heated to about 650F to dry and degrease it, pulverized in a ball mill, and screened through a ZO-mesh screen. The ball mill used for pulverizing the mill scale was 20 inches in diameter and was loaded about half full with 2-inch-diameter steel balls. The-mill scale was ground for to minutes. The aluminum metal (grindings and turnings) was 5 these examples, i.e., much less smoke than was produced by the bare steel surface by comparison. Such a trace corresponds to a smoke rating considerably less than Ringelmann No. l or approximately 5% opacity. No visible smoke at all was observed during the testing of Example 3 and Examples 69. Of Examples ll 1. Example 3'was considered to be the best from the standpoint of no visible smoke being produced and, from a standpoint of overall performance of reaction time and temperature.

screened through a l/2-inch-mesh screen to remove l trash, heated to about 450F to dry and degrease it, pul- EXAMPLE 12 verized in the same ball mill for 20 to 30 minutes, and screened through a l2-mesh screen. The prepared alu- A 1()O-pound sample of an exothermic hot topping miflum d mill Scale for c ampl e b milled composition was prepared in accordance with the comtogether for 3 to 5 minutes, primarily to achieve thor- 20 position of Example 3 reported above employing the ough mixing. Other ingredients were added to the mill ame ingredients, For this purpose, 40 pounds of mill scale and aluminum without any prior preparation. Alscale, 12 pounds of aluminum, 30 pounds raw fire clay, sifer (alloyof about 20% Al, 40% Si and 40% Fe) of 10 pounds of expanded perlite, 5 pounds of fire-clay about 100 mesh, expanded perlite of about lO mesh, grog and 3 pounds of graphite were weighed. These raw fire clay of about l 2 mesh,-fire-clay grog ofabout components were mixed in a small cement mixer while l2 mesh and graphite of about l2 mesh were used about 6.5% by weight water was added very slowly. The where indicated in Table l. The compositions thus pretotal mixing time was approximately minutes. Afterpared were pelletized by rolling the damp mixtures in wards, the damp mixture was screened through a a small cement mixer. The densities of the pelletized /2-inch-mesh screen to break up any large pellets and mixtures of Examples 3-5 and 8-1 1 were about 3943 30 then dried at 350F. The dried, partially pelletized mixpounds/cubic foot and Examples 6-7 were about 8386 ture was packaged in lO-pound lots in polyethylene pounds/cubic foot. The %-inch or smaller pellets were bags. I r

, then tested for their properties as exothermic hot top The material of Example 12 was evaluated on comping compositions and the results are reported in Table mercial steel ingots having a hot top cross sectional l. area of approximately 24 inches square. The hot top- TABLE I 5 Ex Fire- Reac- Reaction Slag Example Mill Aluminum panded Clay Graph tion Temp Condi- Number Scale Grindings Alsifer Perlite Grog ite Time "F tion Smoke 1 45 12 10 3 4'30" 2750 Gummy Trace 2 45 12 l0 3 6'35" 3000 Gummy Trace 3 40 I2 10 5 3 8'20" 3000 Gummy None 4 4o 12 10 s 7'40" 3160 Gummy Trace 5 7 -s 10 3 9'15" 2800 Gummy Trace 6 45 7 8 l0 3 8'0 I 3060 Gummy Trace 7 45 7 8. 10 7'30" 25 Gurnmy None 8 40 7 8 10 2 3 8'30"" 2650 Gummy None 9 40 7 8 10 5 8'0 255p Gummy None 10 40 8 8 10 4 8'45" 2600 Gummy Trace ll 40 12 10 3 5 8'0 3150 Gummy Trace ping material was used in conjunction with insulating boards of-a type commonly employed for commercial operations. One commercial ingot was topped with approximately 20 pounds of the above formula while another ingot was topped with approximately 30 pounds of the above formula by placing two and three bags respectively oflO-pound lots of the formula employed in this example. In both the commercial ingots, the exothermic hot topping material of this example did not produce any visible smoke. Furthermore, the exothermic hot topping composition performed-satisfactorily as an ingot hot topping material.

EXAMPLES 13-20 Compositions containing mill scale, aluminum and fire clay in varying percentages by weight were formulated as listed in Table II. In Examples 13-20, the mill scale particle sizes were of about 2+l0 mesh and the aluminum particle sizes were about 10+30 mesh. The fire clay'particle sizes were approximately -12 mesh. In other words, the mill scale particle sizes were such that the particles passed through a 2 mesh screen and were retained on a 10 mesh screen, whereas the aluminum particles'passed through a 10 mesh screen and were retained on a 30 mesh screen. The ingredients for each of the Examples 13-20 were thoroughly mixed together and then the granular lOOO-gram mixtures of each Example were spread onto lOO-pound molten steel heats having a temperature of about '2900-3000F as in Examples l-l 1. Again, the exotherm of the topping material was measured with an optical pyrometer without correction for emissivity and the results are reported in Table 11,

Table II demonstrates that when the mill scale was varied between 30% and 50% by weight with the aluminum varying between about 10-1 by weight, an exothermic reaction was observed between about 21003 100F. Inthe case of Examples 13-15, no visible smoke was observed. A trace or a faint trace of smoke was observed in Examples 16-17, respectively, but such an amount was less than the bare surface of the metal itself. Furthermore, in connection with Examples 16-17, the negligible amounts of smoke were comparable to the trace amounts of the preceding examples.

In the case of Examples 18-20, wherein the mill scale was present in an amount of about by weight with the aluminum varying between about lO-20% by weight, no reaction was observed within 15 minutes of the test. Accordingly, these examples demonstrate that in accordance with the principles of this invention exothermic smokeless hot topping compositions are provided when the amount of an oxide of iron (mill scale) is within the range of about -50% by weight and the aluminum is in the range of about 9-15% by weight in the presence of a granular inert refractory material. Within such proportions, exothermic hot topping materials are prepared which perform in a satisfactory manner and which will not smoke or only negligible amounts of smoke considerably less than a Ringelmann EXAMPLES 21-27 For purposes of comparison with preceding examples, particularly Examples 13-20, Examples 21-27 were performed. Compositions containing mill scale,

aluminum and fire clay in varying percentages by weight as indicated in Table III were prepared as above.

. However, in Examples 21-27, 80% of the mill scale particle sizes were about l0+ 50 mesh and the-balance was approximately 70% of about l0+l50 mesh and 30% of about l50 mesh. The aluminum particle sizes of Examples 21-27 comprised 85% of about 30+l00 mesh with the balance of 15% being approximately -12+30 mesh. All the test runs in this series were made by placing the exothermic hot topping material on molten steel as in Examples 13-20 above and the temperatures of the reactions recorded by an optical pyrometer as above. The results are reported in Table ll-las follows.

TABLE 111 Ex. Mill Fire Reaction No. Scal Alunii- Clay Temp. F Observation num 21 30 15 2160 No visible smoke 22 40 10 50 2120 No visible smoke 23 40 15 45 2250 No visible smoke 24 50 10 40 2900 No visible smoke 25 30 5 No reaction in 15 minutes 26' 40 5 55 No reaction in 15 minutes 27 10 20 No reaction in 15 minutes Examples 21-24 demonstrated that exothermic hot topping compositions of this invention exhibit no visible smoke while providing an exothermic reaction. Furthermore, particle sizes of oxidizer and fuel are not critically important to the principles of this invention as demonstrated by comparison of the particle sizes of the ingredients in Table III with Tables I-Il. In connection with Examples 25-27 no reaction was observed within EXAMPLE 28 A composition in granular form was prepared and tested according to the procedures of Examples 21-27 except that the formula comprised the following ingredients:

mill scale aluminum -Continued 307: raw fire clay 107: expanded perlitc tire-clay grog 3% graphite on the metal top than the pelletized mixtures used in Examples l-l l. Eliminating the pelletizing step however tends to increase the dust created when the exo thermic hot topping compound was handled. Examples I I I I 5 30-33 also employed the addition ofiron oxide (F8203) Furthermore, the mesh size of the m ll scale in this exf part or a" fth mil] Scale (F3304). These examples p was about mesh and the alumlnulm mosh also demonstrate that Fe O may be substituted for the SIZE was about 15O- p 28 had a roactlon mill scale (Fe O with equivalent results. The Fe O Peraturo of about 320001: and y 11 trace of Smoke used in these experiments was pulverized 'pure F6203 was observed comparable to the trace amounts of the h i a h i f approximately 2() Precedmg exampleshi example thus further 111115" Examples 3440 were conducted for the purpose of Hated that other mesh 51285 otherlha" those opo varying the amounts of mill scale and aluminum fuel abovo o Suitable for use accordmg to the Prmolples with varying proportions of raw fire clay, calcined fire of this mventlonclay, bauxite, or olivine. The raw fire clay and bauxite 15 were calcined before use. The olivine was about 1OO EXAMPLE 29 mesh and composed of magnesium silicate and 7% iron The procedures of Example 28 were repeated except z' The g contlfmed allow l that a mesh size for the aluminum was about -30+150, was a out T 3 AS slerve y ij F; in other words the aluminum particles passed through 20 l i s can use a mesh screen and were retained on a 150 mesh t e OX1 a urt t Z naturfe'o screen. The hot topping composition of Example 29 Sl ag g ance lllsubsmut' had a reaction temperature of about 2950F and exhibhgher li re ractorly men materiel; oa a ited a faint trace of smoke comparable to the trace f zi l chun y or g i pm 15 amounts of the preceding examples. This example fur- 75 we or more easy remova Tom t 6 0t meta ther illustrates the wide latitude of mesh sizes for the EXAMPLES 4 4g oxidizer and the fuel for use in the hot topping compositions of this invention to achieve smokelessness. For h purpose of de mo,nstrdmng that h mesh of the inert filler material 1n the exothermic composition can have an effect on the smokelessness of an exo- EXAMPLES 30-40 30 thermic composition, Examples 4148 were performed This series of exothermic hot topping compositions on an experimental basis. In the case ofthese examples, with varying amounts of ingredients were prepared in 1 200-gram samples of ingredients listed in Table V were accordance with the techniques described in Examples prepared in the form of /2 to inch pellets in a manner l-l 1 except that the compositions of Examples 3040 similar to that described above. The mill scale and aluwere in mixed granular form and not pelletized. These minum were of the same mesh as used in the Examples exothermic compositions as detailed in Table IV here 1-l l. The ignition'time was measured in minutes and inafter were ignited on lO0-pound, induction-furnace seconds required for the ZOO-gram sample to ignite in steel heats in accordance with the procedures of Exama clay-graphite crucible heated to about 2100F. The ples l-l l and the results reported in Table IV. reaction time was recorded in minutes and seconds as TABLE IV Raw Reaction Max Ex. Mill Expanded Fire Time Reaction Slag N0. Scale Alumi Perlite Graphite Clay Other Minutes Temp. F Condition Smoke Remarks num 30 30 12 10 3 30 I0 Fe O l5 2400 Gummy None Some dust 5 fire-clay grog 31 20 l2 l0 3 3O 20 Fe O I6 2400 Gummy None Some dust 5 fire-clay grog 32 l2 l0 3 30 Fe O 9 3000 Crusty Trace Some dust 5 fire-clay grog 33 l2 l0 3 30 36v Fe O I0 2600 Crusty None Trace of dust 9 tire-clay grog 34 40 12 10 3' I0 25 fire-clay 6 3200 Chunky Trace Trace of dust grog 35 40 l2 l0 3 35 fire-clay 8 3100 Chunky Trace Trace of dust grog I 36 40 I2 3 olivine 7 3000 Crusty Trace Few sparks 37 30 I4 3 53 olivine ll/2 3200 Crusty Trace Few sparks 38 30 I4 3 53 bauxite 9 3200 Chunky Trace 39 30 I4 3 53 II 2600 Chunky None 40 30 14 IO 3 43 15% 2540 Chunky None Slag was crumbly underneath Examples 3040 demonstrated the applicability of the'principles of the invention to granular exothermic mixtures. These granular mixtures are more spreadable required for the ZOO-gram sample to complete the reaction. The reaction temperature produced by the reacting exothermic materials at the start and the maximum temperature achieved was measured with an optical py- 'was about 6+35 mesh whereas the fine raw perlite in parative test sample was placed upon a molten steel heat in accordance with the procedures of Examples 21-24. The reaction time was approximately 1 /2 minutes and a maximum temperature of greater than A comparison of Examples 41 and 42 reveal that the composition containing coarse raw perlite (6+35 mesh) of Example 41 did not melt or smoke. In contrast, Example 42 containing the fine perlite of approximately 1.00 mesh did melt and smoke under the experimental test. Furthermore, however, as the amount of aluminum was increased above about 15% by weight to 16-17% by weight (Examples 45-46), even though the mesh size of the raw perlite was coarse, the topping material melted and much smoke was produced. The smoke produced would correspond to a Ringelmann number of. greater than 1, i.e. about 2 or-more. This data demonstrated that for certain compositions it is desirable to employ. a coarser inert granular material and-t maintain the level of aluminum fuel up to about 15% by weight to avoid smoking of the exothermic hot topping compositions.

Quite similarly, where the bauxite was of a finer mesh in Example 43, the topping material smoked considerably under the conditions of test, whereas in Example 44, the coarser bauxite did not smoke. Further, in Examples 47-48, even though the bauxite was ofa coarser grain size (16+80 mesh) with increasing amounts of aluminum from about 16 to 20% by weight in the presence of 40% mill scale the hot topping material developed considerable smoke and melted. The Ringelmann number smoke rating for Examples 47-48 was greater than 1, i.e., about 2 or more.

COMPARATIVE TEST For'purposes of comparison with Examples 21-24 above, a test sample of exothermic hot topping material was formulated employing the same ingredients as the mentioned examples with the same'particle sizes, except that in this comparative test sample, 60% by weight of mill scale was combined with 16% by weight of aluminum and 24% by weight of fire clay. This com- Example 42 was ball milled to about l00 mesh. The 3400F was measured. The composition ofv this test bauxite used in the examples was aluminum ore comsample produced a considerable amount of smoke on posed of impure hydrated aluminum oxide. In Example an order of magnitude greater than Ringelmann No. lv 43, the fine bauxite was approximately 200 mesh, i.e., about 2 or more. This test sample demonstrates whereas the coarse bauxite in the remaining Examples that as the amount of oxidizer is increased above 50% 44 and 47-48 was about 16+80 mesh. The results of to 60% by weight with an amount of aluminum ofabout theseexamples appear in Table V. 16% by weight, considerable smoke is produced.

TABLE V Example Mill Raw fire Ignition Reaction Reaction Temp. "F Slag I Number Scale Alumi- Clay- Other Time Time Start Max Condition Smoke num 41 30 30 Raw Perlite 3'0 3'30" 2200 2250 Not None (coarse) Melted 42 15 30 25 Raw Perlite 2'35" 4'0 2450 3400 Melted Much (fine) 43 15 30 15 Bauxite 4'10" 4'10" 2250 3350 Melted Some (fine) 44 1 30 15 30 25 Bauxite 2'45" 5'0 2150 2450 Not None (coarse) Melted 45 40 16 30 14 Raw Perlite 3'0 3'30" 2200 3200 Melted Much (coarse) 46 40 17 30 13 Raw Perlite 3'30" 2'45" 2200 3400 Melted Much (coarse) 47 '40 16 30 14 Bauxite 2'40" 0'45 3400 Melted Much (coarse) 48 40 20 30 l0 Bauxite 2'15" 0'40 3400 Melted Much (coarse) Thus, in accord with the principles of thisinvention the compositional relationship of both the iron oxide and aluminum fuel must be maintained below certain levels to achieve smokelessness, or a smoke rating of less than Ringelmann No. l or about 5% opacity. Further, complete elimination of visible smoke can be achieved in exothermic compositions where the amounts of oxide or iron and aluminum fuel are controlled in exothermically effective amounts as de-- scribed above and exemplified. It has also been found that alkali nitrates, alkali or alkaline earth metal fluorides, chlorates, or chlorides tend to induce the production of smoke and noxious gasses. Only very minor amounts of such ingredients or similar ingredients can be tolerated in the compositions of this invention be cause of'our findings in order to achieve smokelessness in accord with this inventionilt has been further found that amounts of other oxidizers, particularly heavy metal oxides such as manganese dioxide, and other fuels or ingredients can be tolerated in the exothermic compositions of this invention and the advantages of this invention can be secured. Such variations in view.

' out avoiding the spirit and scope of this invention.

What is claimed is:

proviso that as the amount of iron oxide is increased above about 40% by weight towards about 50% by weight said amount of provided aluminum is decreased towards about by weight and when about 50% by weight of iron oxide is reached then the amount of aluminum is no more than about 10% by weight, and

the balance being predominantly composed of inert finely divided filler material, said oxide, fuel and inert material components proportioned to provide said smokeless composition.

2. The composition ofclaim l which produces no visible smoke during reaction upon the surface of molten metal.

3. The composition of claim 1 which has a Ringelmann number smoke rating of less than one.

4. The composition of claim 2'wherein said metal is iron or steel.

5. The composition of claim 11 wherein said oxide of iron is present in an amount of about 25% to about 45% by weight and said fuel is present in an amount to provide about 9% to about 13% by weight aluminum.

6. The composition of claim 5 wherein granular graphite is present in an amount of about 1-4% by weight.

7. The composition ofclaim 5 wherein said inert material contains an insulating refractory material.

8. The composition of claim 7 wherein said insulating material is expanded perlite.

9. The composition of claim 8 wherein said perlite is present in an amount of about 5% to about 15% by weight.

10. The composition of claim 1 as a hot topping for iron or steel.

11. The composition of claim lv wherein said filler material is a refractory material.

12. The composition of claim 11 wherein said refractory material is selected from the group consisting of raw fire clay, silica flour, silica sand. fire-clay grog, perlite, expanded perlite, olivine, and bauxite.

14 13. The composition of claim 1 wherein said inert filler material has an average grain size of about 1 2 to about +100 mesh. 7

14. A smokeless exothermic hot topping composition for iron or steel consisting essentially of about to about 45% by weight finely divided mill scale, about 9% to about 13% by weight finely divided aluminum, and the balance being predominantly composed of inert refractory material, said mill. scale, aluminum and refractory material components proportioned to provide said smokeless composition. 15. The composition of claim 14 which contains about 1% to about 4% by weight of graphite.

16. The composition of claim 14 which contains about 5% to about 15% perlite.

17. The composition of claim 14 which contains about 40% mill scale and about-12% aluminum.

18. The composition of claim 14 which produces no visible smoke during'reaction upon the surface of a molten metal.

19. A smokeless exothermic hot topping composition for iron or steel having a Ringelmann number smoke rating of less than one which consists essentially of about 35-42% mill scale, about 11-13% aluminum, about 14% graphite and the balance inert refractory material.

20. The composition of claim 19 wherein the inert refractory material contains about 5-1 5% by weight expanded refractory material.

21. The composition of claim 19 wherein said ingredients are granular and homogeneously mixed together.

22. The composition of claim 20 wherein a refractory binder is present to bind said ingredients in pellet form.

23. The composition of claim 22 wherein said binder is fire clay.

'UNETEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,867,155

DATED February 18, 1975 INVENTOR(S) James A. Davis and Arthur R. Elsea It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below. r

Col. 1 Line 40 "969,311" should be -969,33l

Signed and sealed this 27th day of May 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks 

1. A SMOKELESS EXOTHERMIC HOT TOPPING COMPOSITION CONSISTING ESSENTIALLY OF AN EFFECTIVE EXOTHERMIC AMOUNT OF AN AXIDE OF IRON IN FINELY DIVIDED FORM UP TO ABOUT 50% BY WEIGHT, AN EFFECTIVE EXOTHERMIC AMOUNT OF FUEL IN FINELY DIVIDED FORM SELECTED FROM THE GROUP CONSISTING OF ALUMINUM AND ALLOYS THEREOF, SAID AMOUNT PROVIDING UP TO ABOUT 15% BY WEIGHT ALUMINUM, WITH THE PROVISO THAT AS THE AMOUNT OF IRON OXIDE IS INCREASED ABOVE ABOUT 40% BY WEIGHT TOWARDS ABOUT 50% BY WEIGHT SAID AMOUNT OF PROVIDED ALUMINUM IS DECREASED TOWARDS ABOUT 10% BY WEIGHT ND WHEN ABOUT 50% BY WEIGHT OF IRON OXIDE IS REACHED THEN THE AMOUNT OF ALUMINUM IS NO MORE THAN ABOUT 10% BY WEIGHT, AND THE BALANCE BEING PREDOMINANTLY COMPOSED OF INERT FINELY DIVIDED FILLER MATERIAL, SAID OXIDE, FUEL AND INERT MATERIAL COMPONENTS PROPORTIONED TO PROVIDE SAID SMOKELESS COMPOSITION.
 2. The composition of claim 1 which produces no visible smoke during reaction upon the surface of molten metal.
 3. The composition of claim 1 which has a Ringelmann number smoke rating of less than one.
 4. The composition of claim 2 wherein said metal is iron or steel.
 5. The composition of claim 1 wherein said oxide of iron is present in an amount of about 25% to about 45% by weight and said fuel is present in an amount to provide about 9% to about 13% by weight aluminum.
 6. The composition of claim 5 wherein granular graphite is present in an amount of about 1-4% by weight.
 7. The composition of claim 5 wherein said inert material contains an insulating refractory material.
 8. The composition of claim 7 wherein said insulating material is expanded perlite.
 9. The composition of claim 8 wherein said perlite is present in an amount of about 5% to about 15% by weight.
 10. The composition of claim 1 as a hot topping for iron or steel.
 11. The composition of claim 1 wherein said filler material is a refractory material.
 12. The composition of claim 11 wherein said refractory material is selected from the group consisting of raw fire clay, silica flour, silica sand, fire-clay grog, perlite, expanded perlite, olivine, and bauxite.
 13. The composition of claim 1 wherein said inert filler material has an average grain size of about -12 to about +100 mesh.
 14. A smokeless exothermic hot topping composition for iron or steel consisting essentially of about 25% to about 45% by weight finely divided mill scale, about 9% to about 13% by weight finely divided aluminum, and the balance being predominantly composed of inert refractory material, said mill scale, aluminum and refractory material components proportioned to provide said smokeless composition.
 15. The composition of claim 14 which contains about 1% to about 4% by weight of graphite.
 16. The composition of claim 14 which contains about 5% to about 15% perlite.
 17. The composition of claim 14 which contains about 40% mill scale and about 12% aluminum.
 18. The composition of claim 14 which produces no visible smoke during reaction upon the surface of a molten metal.
 19. A smokeless exothermic hot topping composition for iron or steel having a Ringelmann number smoke rating of less than one which consists essentially of about 35-42% mill scale, about 11-13% aluminum, about 1-4% graphite and the balance inert refractory material.
 20. The composition of claim 19 wherein the inert refractory material contains about 5-15% by weight expanded refractory material.
 21. The composition of claim 19 wherein said ingredients are granular and homogeneously mixed together.
 22. The composition of claim 20 wherein a refractory binder is present to bind said ingredients in pellet form.
 23. The composition of claim 22 wherein said binder is fire clay. 